Hybrid Solar Panel: Heat Water + Generate Electricity

sunshine_eggo said:

I expect the added panel structure and heat exchanger is notably heavier than the water.

Similar product, though I don't see the thermal rating:

aHtech 72SK Hybrid Photovoltaic and Thermal PVT Solar Panel (in Stock)

Hybrid Photovoltaic and Thermal PVT Solar Panel, generates both electiricity and hot water. Ships Canada/US wide, to order please call +1 (888) 686 7652.

hydrosolar.ca

2sq-m meters.
110 lb
hold 1/2 gal of water or about 4 lb

So about 2.5X a typical 2sq-m panel.

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My weight reference was for my diy approach.
I'm sure that heat sinks and multiple loops per panel would definitely add up.

110LBS each panel.......plus fluid....... fittings, etc.....

Hmmm. I thought this combo had been discussed many years ago, and it was deemed that PVs and thermal solar collectors don't "play" well together. Mostly because the temps that most thermal collectors reach is too high for efficient PV operation.

I know my thermal DHW panels typically run at 140F+ on a sunny day when heat is being moved to the storage tank (e.g. water is being circulated in the panels), so that is the temp they would "cool" things to. When the storage tank is at it's max temp (~160F) and the pump stops and the panels get to 180F+, higher on sunny summer days. I know that PV panels can get quite toasty too in the sun, but I don't think that DHW system circulating under them is going to provide much cooling, especially if you are leaving the water in collector long enough to get a good temp rise that you need for most thermal heat exchangers.

I suppose if you used HP tech to extract more of the heat from the water, then you might get better cooling on the PVs, since the return water would be cooler. Or if you increase the water flow rate so that it does not rise as much in temp on each pass. But with passive heat exchangers it does not seem that it can work. Just thinking out loud here, but I have my doubts...

Will have to go out and measure the return water temp on the DHW loop and the surface and back temps of the PVs, to see if my assumptions here are still valid.

Uncooled cells are sitting at about 113, which is very warm water. Hot water tank hot? No. Would you want to bathe in it? Not for long. If the panel regulates flow to yield typical PV performance and yields 113-ish water, that still feels like pretty big win.

grizzzman said:

110LBS each panel.......plus fluid....... fittings, etc.....

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Assuming a 15 x 40 foot roof face and a wet snow, your roof already supports over 2000 pounds for every inch of snow.

Brett V said:

Assuming a 15 x 40 foot roof face and a wet snow, your roof already supports over 2000 pounds for every inch of snow.

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Yeah... In the county HBR resides, 40# snow load.

That means a roof in my area must be built to support 855# on an area equivalent to a single 2sq-m PV panel (about 400W).

Just another PIPE dream.

sunshine_eggo said:

Uncooled cells are sitting at about 113, which is very warm water. Hot water tank hot? No. Would you want to bathe in it? Not for long. If the panel regulates flow to yield typical PV performance and yields 113-ish water, that still feels like pretty big win.

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That sounds about right. Have not gotten a sunny day yet to check numbers here. And you are right, if you were running water behind the panels to extract the heat, the water would likely run ~100F. Which would mean the solar hot water tank could not be heated much above that (typically ~10F less than the incoming hot water) with passive heat exchangers. If you had a water to water heat pump, you should be able to get to decent DHW temps (>120F) from that 100F collector water, but very few people will be willing to take a shower in 100F water.

Finally had a mostly sunny day to get some temps from my systems. Here's what I measured today roughly at noon:

PV panels temp - 48F
SHW panel temp - 121F (actually water exiting at the top of the panels, panel probably higher)
PVs production - 70% of rated power

Outside conditions 36F with 3mph wind

This is a January day in the Rockies, but these ground mounted panels stayed considerably cooler than the hot water panels under the same sunlight. No cooling advantage at all to be gained by putting "cooling" water behind the PVs. Results would likely be less dramatic at summer temps, but even then, at my location, outside air temp is rarely above 80F and the SHW panels soar to 160-180F.

No doubt things would be somewhat different for roof mounted PVs. But if you put this PV/SHW "sandwich" panel in an insulated box (which you need to do to get the most heat into the water), then I don't think you will see much if any cooling effect from having the water on the PV. And if you don't insulate the sandwich, you're not going to realize much hot water gain. Think it is still best to keep these two solar panels separate.

This is just a way to shorten the usable life of a PV array.

Far better to keep solar thermal and solar PV separate as the latter will last a lot longer than the former.

And frankly, it's just cheaper and far more effective to heat water using solar PV + air source heat pump water heater.

You are all forgetting this technology exists and works in Australia not necessarily here.

Quattrohead said:

You are all forgetting this technology exists and works in Australia not necessarily here.

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Pretty much no-one here uses it though. It an expensive solution to a problem which doesn't exist.

Solar thermal on its own was popular 10-20 years back when PV was expensive, and there are still hundreds of thousands of systems in place, and many of those homes also have solar PV. But solar thermal water heating installation numbers have been in decline for a decade because it's too expensive.

When the time comes to replace their solar thermal water heater, people are instead going for electric water heating powered by grid-tied PV, either using a heat pump water heater or resistive element if they have ample excess PV. It's cheaper, more effective, flexible and robust than combining solar thermal with PV.

Good to know from the horses mouth. I guess the world is bigger than the USA haha

This combo panel just seems like a gimmick. I think @wattmatters has it right given the price of PV these days: Use it to power an air source heat pump water heater and call it a day.

There seems to be a human fascination with combining things, as evidenced by the popularity of AIO inverters. That may be a good idea on install day, but it's a terrible idea when somethings (inevitably) fails.

IMHO it may grab headlines, but the practicalities (especially re temperature of the water as mentioned above). Then you'd need both electricians and plumbers to work with one panel (OK for us DIYer's, but imagine co-ordinating tradesmen)

But the biggest catch I think is that typically you only need 4 or 5 water panels but at least 12+ PV panels. So, you'd have to match 5 dual panels with a different type of PV panel.

And what about failure rates + having to fix both together. Doesn't add up to me.

Madcodger said:

There seems to be a human fascination with combining things, as evidenced by the popularity of AIO inverters.

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Some things work very well when combined. e.g. think of all the items many people no longer have because they have an iPhone. I no longer have calendars, a camera, a video recorder, clock/timer, stopwatch, GPS nav units, music players, and almost replaced banking cards.

AIOs are sort of in the middle, and decent ones work OK. It depends on the circumstances. When I put something on a roof, I'm looking for decades of reliable performance. I have a different expectation of longevity from an AIO, while any replacement is a relatively simple exercise.

AIOs provide convenience and simplicity, which are useful product traits. I see neither convenience or simplicity with these combination solar panels.

I am one of the old school folks with a 25 year plus solar thermal panels on roof (PV powered pump no less) and PV next to it. I cant recomend new SHW panels due to cost but keep an eye out on craigslist and used panels freqently appear for cheap. The weak lin in those systems were the check valves intended to stop thermosyphonIng at night. If the check valve fails open on cold night the antifreeze will suck the heat out of the heat exchanger and freeze it leading to flood in the utility room. That only happens once and the system is taken out of service as no one knows how to work on them or maintain them. That and the controllers have a finite life usually due to failure of an internal component like a capacitor.

Conventional panels typically can get up to 80 deg F over the daytime ambient. Any more than that and the fluid entering the panels radiate more heat than they absorb. Evac tubes can go higher but most evac tube systems are lucky if half the tubes are still vacuum sealed and the supplier is long gone so no replacing them unless they take their chance buying them used.